Certain high-end computer systems often need very large mass storage capacity. In such systems, the mass storage media or devices are housed within one or more cabinets or frames, each containing banks or columns of storage shelves and drive units. The data storage media includes devices such as magnetic media (magnetic tape or disks), optical media (optical tape or disks), and electronic media (PROM, EEPROM, flash PROM). The data storage media are generally contained within modular cartridges, which may be stored in one of the storage shelves or slots when not in use. When a particular data media is needed or selected by the computer system, a robot accessor retrieves the selected data storage cartridge from the storage shelves and inserts it into an available data storage drive for access by the computer system. It may be necessary to return one of the cartridges, which is not presently in use, from the drive units back to the storage shelves, to make room for the selected cartridge.
The combination of one or more frames containing the mass storage media constitutes an automated data storage library. The mass storage system may be arranged in multiple libraries. The data storage media are logically and physically arranged in the frame(s) and library(ies) for efficient configuration and access. The modular cartridges are easily and readily movable between the storage slots and drive units to provide more overall data storage capacity and convenience of maintenance.
As part of routine operations, the automated data storage libraries commonly perform an inventory operation wherein the library reads identifying information about the data storage media, as well as the physical and/or logical locations of the media within the library, in order to verify the contents and configuration of the library. Each cartridge or data storage media has an identifier. The library provides such inventory information to a host computer upon request. An inventory of the entire library is usually performed after power-on or reset operation. A partial or re-inventory of individual frames is performed when a specific frame door has been opened, and subsequently closed, indicating some level of access to the data storage media within the frame. The inventory process involves updating and confirming an inventory database, which keeps track of the cartridges within each frame and the present location of each cartridge within a given frame. The inventory operation is time consuming and disruptive to the library operations and, as such, should be performed only when necessary.
The physical implementation and arrangement of the frames are such that it is possible for a technician or operator to open the door of one frame and reach around or through the frame interface to move, insert, remove, or otherwise access a data storage media contained within an adjacent frame, without opening the door of the adjacent frame. Because the door of the adjacent cabinet has not been opened, there is nothing to indicate that any media contained within the adjacent frame has been accessed or changed. Consequently, the inventory database for the library shows that the adjacent frame and its data storage media are intact and untouched. This type of undetected access can cause disruption to library operations because the inventory reported to the host computer, as well as the inventory maintained by the library, does not match the actual state of the library.
One solution involves the use of path sensors to tell when an area of the library has changed. For example, an optical emitter/detector pair may create a beam of light across a group of storage slots. A break in the beam indicates that the media may have been moved, inserted, or removed from the group of storage slots. One problem with the optical detector solution is the additional cost of installing and maintaining the emitters, detectors, cabling, mounting and interface circuits, which is compounded with large libraries that would require a correspondingly large number of such emitter/detector pairs. The emitter/detector pairs often require periodic alignment and cleaning to remove accumulation of foreign particles from the light lenses and sensors. The potential for failure of the emitters, detectors, cabling, connectors, and interface circuits creates an ongoing maintenance issue.
Another solution is to provide an inventory of one or both adjacent frames, as a matter of procedure, when a particular frame door has been opened. The process of inventorying two or more frames, when only one frame door is opened, increases the associated re-inventory time. Most data storage libraries use competitive comparisons, which includes a measure of how quickly the system can perform an inventory operation and get back on-line after an open frame door is detected. Any solution that materially increases inventory time is not desirable.
Another approach is to provide a manual inventory selector, such as an operator panel control, that allows the operator or technician to manually schedule re-inventory of adjacent frames when another frame door has been opened. However, the manual selection to inventory certain frames involves human action and may be forgotten or missed because of training issues. As a result, the manual selection is not likely to be made until after the library has already been disrupted by the media change. As customer expectations move toward a continuous availability of the library, i.e., the well known “24×7” goal, it is increasingly important that routine user interaction with the library does not unnecessarily disrupt host/library operations.
What is needed is a method to prevent disruption to host/library operation after media has been moved, inserted, or removed from a frame adjacent to a frame that has experienced a door open and closure, without affecting nominal library performance, and without requiring foresight on the part of the customer to anticipate such inventory errors.